In wireless communication systems, such as the long term evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) Terrestrial Access Network (UTRAN) in 3rd Generation Partnership Project (3GPP), new functionalities or features for data channels, such as fast link adaptation, hybrid automatic repeat request, or fast scheduling in case of high speed downlink packet access (HSDPA), rely on rapid adaptation to changing radio conditions. To implement these features, a control channel is used to carry control information relevant for those terminal devices (or user equipments (UEs) in 3G terminology) for which data is available on the respective channel.
An adaptive modulation and coding concept may be applied to the control channel to expand the dynamic range of the control channel. One of the problems with the power control option is that only a certain dynamic range can be exploited due to hardware limitations.
To support different data rates a range of channel coding rates and different modulation formats may be supported. Hence, at least two formats, e.g., modulation and coding scheme (MCS) formats, may be supported for the control signaling via the control channel. The downlink (DL) control signaling may be located in the first n transmission symbols. Thus, data transmission in DL can at the earliest start at the same transmission symbol as the control signaling ends.
FIG. 3 shows an example of a design of one “mother” control channel out of a plurality of control channels. This mother control channel can be split into some “child” control channels by dividing the physical resources using a variable coding scheme for allocations. In this example, the channel size of a “mother” control channel is 360 channel bits which may correspond to 180 QPSK (quadrature phase shift keying) symbols. However, it is noted that the number of channel bits is a design parameter which may be used to adjust tradeoff between coverage and capacity. In FIG. 3, the upper part shows a case in which one user is allocated to the control channel, while the lower part shows a case in which two users are allocated within the same physical resources, each using a “child” control channel, corresponding to 180 channel bits following the abovementioned example. The control information conveyed via the control channel may be divided into allocation information 42 for the terminal device, a terminal identification 44 (e.g. user equipment identity (UEID), cell-specific radio network temporary identity (C-RNTI) etc.), and an error checking pattern 46 (e.g. cyclic redundancy check (CRC)). It is noted that the terminal identification 44 and the error checking pattern 46 may be merged, such that a terminal or user specific masking of at least a part of the error checking pattern can be achieved.
A problem faced when decoding the control channel is that the receiving end will have to know the size and/or length of the data information being decoded (in order to do channel decoding and error checks) prior to the actual decoding. To illustrate, a situation is assumed where downlink allocation uses 80 bits. In the upper case of a single user and a channel size of 360 channel bits, an effective code rate of about 0.2 (i.e. 80/360=0.22), while in the lower case the effective code rate is increased to about 0.4, by reducing the channel size to 180 bits and still keeping the downlink allocation size to 80 bits. Now, if there are two formats available for the control signaling, the amount of users for downlink using format #1 and format #2, respectively, must be determined in order to know the size of each. The same applies to the allocations for the uplink direction.
This information could be forwarded for example as separate category 0 information (control information for the control channel). However, in the case of having two formats for the control signaling (as described above), at least four numbers are needed to indicate the amount of allocations in each ‘size/type’ of allocation.